One objective of this research is to further delineate the effects of acute leukemia and cancer chemotherapeutic agents on certain factors influencing growth in children, especially as related to the hypothalamic pituitary target organ system. This data will be used to better explain the mechanism of growth retardation observed during intensive therapy; to explain the delayed adolescence and growth retardation seen in some children who were treated but have now been off therapy for several months, and to determine if complete suppression of the hypothalamic-pituitary-target organ system can be an explanation for the prolonged remission observed in some children. A further objective will be to determine if a specific end point can be obtained for determining adequacy of chemotherapy, especially of the central nervous system, without over-kill. Hypophysectomy has been shown to delay the development of leukemia, and the administration of growth hormone negated this delay. This implies that success of treatment of leukemia may depend on how efficiently the synthesis and/or release of growth hormone is blocked. Thus, a study to assess the hypothalamic-pituitary axis, especially growth hormone and somatomedin in children with acute lymphocytic leukemia before, during, and after chemotherapy, may be a valuable aid in evaluating adequacy of therapy and may allow quantitative biologic assessment of hypothalamic function for evidence of tumor involvement and/or suppression by various therapeutic modalities. The present studies propose to evaluate these factors after certain therapeutic schedules as defined by the Southwest Oncology Group study (SWOG), and to continue efforts to isolate and purify somatomedin such as to develop a more rapid sensitive assay.